Man-made structures such as watercraft hulls, power station cooling water inlets and outlets, buoys, oil drilling rigs and all manner of surfaces immersed or splashed by fresh and/or sea water are prone to fouling by aquatic organisms such as barnacles, mussels, green and brown algae and the like. The fouling caused by organisms adhering on mobile structures such as watercraft hulls impedes the movement of the craft through the water. Static structure fouling hampers inspection and modification, in addition to having untold effects on the wave energy absorption by the structure. Piping systems become narrowed through accumulation of organisms with the result of reduced flow rates and increased wear on pumping equipment.
To combat fouling, considerable attention has been directed to the development of improved RTV silicone rubber compositions. Ideally, an RTV is stable for an indefinite period when stored in the absence of moisture, and rapidly cures to a tack-free coating upon exposure to moisture. A problem typically associated with RTV silicone rubber coatings is the difficulty in making them adhere well to substrates. This problem is discussed in European Patent Application 16195, which proposes applying the RTV silicone rubber as a cladding on a fabric backing. This method necessarily introduces additional complexity associated with rubber application to the backing and smoothing the backing onto the substrate.
An alternative approach involves the various primer compositions applied to the substrate as an undercoating for an RTV silicone rubber. Such primers have included a cross-linkable silicone paste (U.S. Pat. No. 3,702,778). Primers have also been devised using mixtures of epoxy-silane and an alkene-containing silane, polyurethanes, various rubbers, aminosilane-containing silicone resins and chlorinated polyethylene for a limited class of surfaces.
The commercially most successful primers for RTV silicone foul-release rubber contain substances toxic to aquatic organisms. The metal containing catalysts necessary for curing of such primers is typically a source of such toxins. Because of the leaching of toxins from such coatings, otherwise useful primers are increasingly being regarded with disfavor. As a result, a need exists for a primer which does not contain markedly toxic materials.
Prior art primer compositions have relied on metal containing catalysts and in particular tin-based catalysts such as dibutyltin dilaurate and tributyltin chloride to speed the cure of a primer. U.S. Pat. No. 5,290,601 is a representative example of such a composition. The concentration of a metal-containing catalyst is a result of a compromise between pot life of the mixed material and the curing time of the coating once applied. Thus, the higher the catalyst concentration the shorter the pot life with an ensuing increase in cure rate. Conversely, low catalyst concentration may result in the cure reaction being incomplete and resulting in a high-tack, low molecular weight primer with unacceptable material properties.
A stop gap solution to obtain long pot life, fast cure times and avoid undue contact with undesirable metal catalysts, especially those containing tin, has involved separate packaging of the catalyst material. The net result of which being additional handling procedures.